This invention relates to a method of making a power transmission belt having transversely extending driving teeth on opposite surfaces thereof and to an assembly for making such a belt including a flexible matrix of special construction for forming a toothed portion of the belt. This invention also relates to a power transmission belt having driving teeth on its opposite surfaces manufactured by the method and assembly and more particularly this invention relates to such a belt having a war-resistant facing covering the driving teeth on each opposite surface.
Belts having teeth in opposite surfaces are not new in the art. For example, Waugh U.S. Pat. No. 2,699,685 relates to a V-type transversely grooved power transmission belt having alternating grooves and cogs in opposite surfaces thereof to increase its flexibility in a belt drive. These cogs or teeth, however, do not function to drive the belt so that there is no need that the teeth be precisely formed and positioned as is the case when the teeth serve a driving function as in a timing or gear type belt such as a positive or synchronous drive belt.
Synchronous drive belts having teeth in both driving surfaces also are not new. It has been customary to mold the driving teeth in one surface of such a belt and grind the driving teeth in the opposite surface to achieve an accurate alignment of the teeth in one surface of the belt in relation to the teeth in the opposite surface. This procedure has resulted in a generally satisfactory product but has proven to be costly. This procedure also has an additional disadvantage since it is not practical to provide a wear-resistant facing, for example of a rubber impregnated textile fabric material, covering the surface of the belt to which the driving teeth have been ground or cut.
One problem in making a synchronous drive belt which has teeth molded on its opposite driving surfaces so that a wear-resistant facing can be provided on both surfaces is that it is extremely difficult to align the teeth of one surface in relation to the teeth of the opposite surface and to retain the configuration of the teeth as the belt is being manufactured. Adams U.S. Pat. No. 3,673,883 discloses a method of manufacturing a power transmission belt having driving teeth in each surface with a coating of an elastomeric wear and abrasion-resistant material covering the teeth of each surface. However, this patent does not disclose a method of solving the problem of tooth alignment and retention as discussed above.